Bug description

Hi, I was about to create a custom plugin.
Trying to build a custom build (tom-select.custom.js) fails with the following error:

> [email protected] build
> grunt build --plugins=remove_button,restore_on_backspace

... snip uninteresting parts ...

> [email protected] build:js:esm
> tsc -p .config/tsconfig.esm.json

src/tom-select.custom.ts(2,23): error TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean './tom-select.js'?
Warning: Command failed: npm run build:js
 Use --force to continue.

Aborted due to warnings.

The issue is that the generated tom-select.custom.ts imports ./tom-select without the .js extension.
It's an easy fix and I can create a PR if interested.

Expected behavior

Running npm build with the --plugins option should complete successfully without TypeScript errors.

Steps to reproduce

1. Clone the repo, get on master branch
2. Run npm install
3. Run npm run build -- --plugins=remove_button,restore_on_backspace
4. See error: TS2835: Relative import paths need explicit file extensions in ECMAScript imports when '--moduleResolution' is 'node16' or 'nodenext'

Additional context

• OS: macOS 15.5